Papermaking machines



y 4, 1963 D. G. TRETHEWAY ETAL 3,089,409

PAPERMAKING MACHINES 4 Sheets-Sheet 1 Filed June 12, 1961 y 4, 1963 D. G. TRETHEWAY ETAL 3,089,409

' PAPERMAKING MACHINES Filed June 12, 1961 4 Sheets-Sheet 2 May 14', 1963 D. e. TRETHEWAY ETAL 0 PAPERMAKING MACHINES Filed June 12, 1961 4 Sheets-Sheet 4 Patented May 14, 1963 3,089,409 PAPERMAKING MACHINES Donald G. Tretheway, Neenah, and Richard O. Hansen,

Menasha, Wis, assignors to Kimberly-Clark Corporation, Neenah, Wis, a corporation of Delaware Filed June 12, 1961, Ser. No. 116,329 3 Claims. (Cl. 100-162) This invention relates to improvements in rotary de- Watering presses employed for crushing and macerating wet bark and other fluid-containing fibrous materials, and expressing fluids therefrom.

A primary object of the invention resides in the provision of an improved press roll construction adapted to increase the capacity of present bark dewatering presses.

A further object is to provide an improved bark de- Watering press roll capable of performing satisfactorily for a substantially longer service life than rolls of currently employed construction.

An additional object is to provide a multiple element press roll which may be quickly disassembled for replacement or repair of damaged portions, thereby effecting substantial cost savings over the present practice requiring replacement of the entire roll.

Other objects and advantages of the invention will become apparent from the accompanying description and drawings.

FIG. 1 is a diagrammatic view in elevation of a conventional three-roll bark press arrangement.

FIG. 2 is a partial axial section showing the circumferential grooving and sectional structure of a feed roll incorporating the invention.

FIG. 2A is a section taken at AA of FIG. 2.

FIG. 3 is a partial axial section of a top press roll.

FIG. 3A is a section taken at AA of FIG. 3.

FIG. 4 is a partial axial section of a discharge roll.

FIG. 4A is a section taken at AA of FIG. 4.

FIG. 1 illustrates a conventional dewatering press arrangement, such as is employed for processing Wet bark or for milling sugar cane, equipped with rolls modified to incorporate therein the improvements of this invention. The press arrangement includes the usual feed roll 20', top press roll 30 and bottom discharge roll 40. In conventional construction, all rolls normally are of cast iron, and are manufactured by unitarily casting a rough blank and thereafter finish machining the blank to provide a plurality of circumferential grooves therein as shown at 21, 31, and 41. In this invention, the grooved rolls are of segmented construction as illustrated in FIGS. 2, 3, and 4, hereinafter described in more detail. The grooves 21, 31 and 41 are of V configuration in axial section. The rolls are mated for complemental registry of the grooves, with suitable clearance therebetween. The land areas 28 and 38 in the surface of feed roll 20 and top press roll 30 are normally provided with circumferential'ly spaced depressions 27 which provide a toothed effect to assist in advancing the bark through the press.

In operation, bark is fed to feed roll 20 by conveyor 4. The press rolls are supported in suitable hearings to permit application of pressure to the top roll 30. Bark, or the like, is fed by feed roll 20, into a nip 7, formed intermediate top roll 30 and feed roll 20, where the bark is crushed, macerated and dewatered. The expressed fluid escapes through fluid removal channels disposed circumferentially of the feed roll such as are shown at 22 in FIG. 2.

Associated with the press rolls is a channel forming turnplate 5 over which the macerated and dewatered bark moves to be fed into nip 6 for further pressing'and maceration before being discharged. Scrapers 8 and 9 aid in removing macerated material from the surface of rolls 30 and 40. Turnplate 5 and scrapers 8 and 9 are transversely serrated in conformity with the respective grooved rolls.

Sand and grit, usually present in bark or sugar cane stock, gradually polishes the surfaces of conventional type rolls and causes substantial reduction in press capacity due to reduced friction between the roll surfaces and the stock. When these conventional rolls are dam-aged as a result of large pieces of junk metal or stone passing through the press nips, it is necessary to replace the entire roll or rolls at considerable cost.

The actual physical arrangement of the press rolls in relation to each other, and operation of the illustrated bark press is conventional and does not constitute a part of this invention.

FIGS. 2, 2A, 3, 3A, 4 and 4A show press roll constructions embodying one form of the present invention which overcomes the above disadvantages.

Feed roll 20, of an improved construction as shown in FIG. 2, includes a series of steel discs or annular segments 29 with evenly spaced circumferential grooves 21 therein. Roll 20' is also provided with optional fluid removal channels 22 disposed peripherally of the side margins of each segment, through which is discharged fluid as it is squeezed from the treated fibrous material. In the particular embodiment shown, the roll consists of a 36" wide roll, with 12 annular 3" segments having three grooves 21, and four land areas 28, each. The width of the steel disc segments, the spacing of the grooves, and the number of grooves per ring segment, may be varied and still fall within the scope of this invention.

The land areas 28 of the grooved configurations in the feed roll surface are preferably provided with cut-out depressions defining teeth 27 which aid in macerating and moving the bark through the press.

For the purpose of counteracting the polishing effect of the feed stock on the roll surfaces, which has heretofore resulted in substantial reduction in capacity and necessitated frequent roll changes, the surfaces of the circumferential grooves are coated with a cemented carbide such as a fused and hardened coating of tungsten carbide -grit 23. The carbide coating may be from about 0.010" to 0.050 in thickness. The preferred thickness of the coating is about 0.030.

Steel discs 29 are held together with tie-bolts 24 and keyed to a central core 25 by key 26 to make up the press roll. Various other methods of assembling discs into unitary rolls may be used.

Top roll 30, similar in construction to feed roll 20, is provided with evenly spaced circumferential grooves 31, but the fluid removal channels usually are not provided therein. The surface of the circumferential grooves, however, are also preferably coated with tungsten carbide grit 23.

Discharge roll 40 is similar to top roll 30 but normally does not have the cut-out depressions or teeth portions in the land surface areas. The outer surface of this roll is preferably, but not necessarily coated with tungsten carbide grit 23 as are rolls 20 and 40. Since work forces imposed 'on roll 40 are less severe than on rolls 20 and 30, roll 40 alternately may be provided with flame hardened steel surfaces or the like. In applications where the material operated on is relatively free of abrasive material, a segmented steel roll structure having rough, fiame-harsdened working surfaces, Without carbide coating, may be employed advantageously.

The press roll ring segments are preferably cast from mild steel or heat treated steel alloy with the V-grooves cast rough to enhance their frictional gripping surface. Alternately, the segments may be flame cut from steel plate with the grooves and teeth portions subsequently machined therein. A base steel of less than 30 points carbon is suitable. More than 30 points carbon may be used but is not as desirable when carbide coating is contemplated since it results in excessive carbon entering the carbide coating.

When the tungsten carbide grit coating is applied, known spraying techniques are employed. Each ring segment is preheated to approximately 400 F. prior to spraying. Preheating reduces loss of powder during spraying and eliminates thermal shock break up of the particles as sprayed. The spray is applied by spray guns held normal to the grooved surface as the work is turned in a suitable lathe at about 20 to 30 ft. per minute. the spraying operation the spray gun is arranged in two positions to effectively cover each side of the V-grooves. Up to about 0.010" of carbide coating can be applied in a single pass. Suitable cemented carbides for use as the coating are available on the market under the tradename Kennametal. Various grades are obtainable for this purpose ranging in Rock-well C hardness of from about 75.0 to 82.0 and transverse rupture strength of from about 150,000 p.s.i. to 325,000 p.s.i.

The work piece is preferably grit blasted and thoroughly cleaned prior to spraying. The grit blasting provides improved mechanical bond before fusing. Surfaces not to be covered by the carbide coating are coated with Welders paint for easy removal of unwanted coating.

After spraying the work piece is placed in a furnace and raised to a temperature of approximately 1900 for fusing. It is important to control the maximum temperature closely. Excessive temperature will cause the coating to run. No soaking at maximum temperature is required or desired. As soon as the Work piece itself, not just the furnace, is at the required temperature, it is removed from the furnace and air-cooled.

Heat distortion may be corrected after heat fusing by final machining of surfaces other than the hardened areas. Spot repairs are possible. If a groove is damaged due to an abnormal condition, the base material can be Welded and machined to the desired configuration. The repaired surface is then grit blasted, preheated as above, and the carbide spray applied. The repaired area is fused by torch.

Thin and worn surfaces can be rebuilt by repeating the original application procedure.

For

Press rolls made according to this invention have an unusually long life, are easy to maintain and repair, and increase the capacity of bark presses due to the rough friction surfaces provided on the rolls and general abrasion resistance of such surfaces.

While the invention is specifically directed herein to bark presses, the improved press rolls are equally adaptable for use in sugar cane or bagasse mills.

Modifications within the scope of this invention will become readily apparent to those skilled in the art.

What is claimed is:

1. In a macerating and dewatering press having circumferentially grooved press rolls, a press roll structure comprising an assembly of annular mild steel segments, and a fused coating of spray-applied cemented carbide grit on the grooved surfaces of said segments to provide an abrasion resistant rough friction surface.

2. A macerating and dewatering press roll having a grooved annular surface, said press roll comprising an as sembly of cast annular segments of mild steel containing less than 30 points carbon, the surface of each of said segments being circumferentially grooved, the grooved surface of each of said segments having a spray-applied coating of cemented tungsten carbide grit fused thereon to provide an abrasion resistant rough friction surface.

3. In a macerating and dewatering apparatus having circumferentially grooved press rolls, a pair of coacting, nip-forming rolls each comprising an assembly of annular segments of mild steel, the surface of each of said segments being circumferentially grooved, the grooved surface of each of said segments having a spray-applied coating of cemented tungsten carbide grit fused thereon to provide an abrasion resistant rough friction surface.

References Cited in the file of this patent UNITED STATES PATENTS 250,720 Faure Dec. 13, 1881 571,264 Culver Nov. 10, 1896 673,768 Fleming May 7, 1901 1,743,623 Ross Jan. 10, 1930 2,167,544 De Bats et al. July 25, 1939 2,714,563 Poorman et al. Aug. 2, 1955 

3. IN A MACERATING AND DEWATERING APPARATUS HAVING CIRCUMFERENTIALLY GROOVED PRESS ROLLS, A PAIR OF COACTING, NIP-FORMING ROLLS EACH COMPRISING AN ASSEMBLY OF ANNULAR SEGMENTS OF MILD STEEL, THE SURFACE OF EACH OF SAID SEGMENTS BEING CIRCUMFERENTIALLY GROOVED, THE GROOVED SURFACE OF EACH OF SAID SEGMENTS HAVING A SPRAY-APPLIED 